As is well known to those skilled in the art, middle distillates such as diesel oils, cracking stocks, and catalytic cycle oils as produced are characterized by various deficiencies including poor cetane number and burning quality.
It is common to attempt to improve the quality of these hydrocarbon stocks by extracting the undesirable components which are responsible for the deficiencies. These stocks may for example be treated with furfural which may extract aromatics, olefins, and compounds of nitrogen, oxygen, and sulfur from the middle distillate oil. The treated oil is typically characterized by improved properties.
Furfural treating of these charge oils is typically carried out by contacting 100 parts of deaerated charge oil (typically having an ibp of 350.degree. F.-475.degree. F., say 375.degree. F. and a 50% bp of 500.degree. F.-600.degree. F., say 550.degree. F. and an ep of 600.degree. F.-750.degree. F., say 650.degree. F. and an aromatics content of 10-40 w %, say 30 w %) with 50-250 parts, say 110 parts of furfural. Contact is commonly at 70.degree. F.-150.degree. F., say 110.degree. F. at 40-120 psig, say 100 psig in a contacting operation which may be carried out in a rotating disc contactor.
The raffinate (commonly containing 75.90 w %, say 83 w % oil and 10-25 w %, say 17 w % furfural and aromatics content of 5-25 w %, say 12 w %) is commonly recovered at 400.degree. F.-450.degree. F., say 430.degree. F. and passed to a series of stripping towers and vacuum flash towers to separate refined oil and furfural.
The extract stream (commonly containing 20-50 w %, say 30 w % oil and 50-80 w %, say 70 w % furfural and aromatics content of 70-90 w %, say 80 w %) is commonly recovered at 380.degree.-450.degree. F., say 420.degree. F. and passed to a series of stripping towers and vacuum flash towers to separate extract and furfural.
The several furfural streams recovered during these operations are further passed to a series of separation and fractionation operations wherein furfural is recovered and recycled to the contacting operation e.g. the rotating disc extractor.
It will be apparent that a substantial portion of the cost of a furfural treating unit lies in the several distillation columns and associated equipment including fired heaters, heat exchangers, pumps, etc; and the cost of operation is clearly large because of the cost of heat and power associated with these operations.
It is an object of this invention to provide a novel process for furfural treating of middle distillates. It is a particular object of this invention to provide a process which minimizes the need to provide distillation steps and which permits substantial savings in operating costs. Other objects will be apparent to those skilled in the art.